[Tutor] Dynamic inheritance?

[Alan Gauld]

> import Templates
>
> self.site_name = 'SiteA'
> self.template_type = 'Page'
>
> self.template = ???

How about a dictionary holding references to the classes against their 
names?
The dictionary could be a class attribute of the top level superclass or a 
module
level dictionary. It should be updated ideally by the class definition or 
more
simply by hard coding a registration fuinction.

Something like

class Root:
   subclasses = {'Root': Root}
   @classmethod
   def registerSubclass(name, aClass):
        #could check it really is a subclass here...
        Root.subclasses[name] = aClass

class Sub(Root):
    pass
Root.registerSubclass("Sub",Sub)

Now your code becomes:

 self.site_name = 'SiteA'
 self.template_type = 'Page'

 self.template = Root.subclasses[self.template_name]()  # instance of Page

In fact it could just be a dictionary of templates, it needn't be subclasses
at all, however for the sake of clean polymorphism its probably better
if they are.

HTH

Alan G.